Segmented oligonucleotides based on short interfering RNA (siRNA) have been evaluated for RNA interference (RNAi) activity. Leuschner et al., (2006 EMBO 7:314) described an RNA-induced silencing complex which has a discontinued passenger (or sense) strand and a 2′-O-methyl modified nucleotide at position 9 of the passenger strand (5′ to 3′), the natural cleavage site. Bramsen et al., (2007 Nucleic Acids Res. 35:5886) described an RNAi-active siRNA molecule comprising an internally segmented passenger strand, where the nick or gap is not necessarily located at the natural cleavage site, stabilized with locked nucleic acid (LNA) modifications at a number of positions. See also, e.g., Wengel et al., PCT Publication WO 2007/107162 A2; Quay et al., PCT Publication WO 2008/049078. None of Leuschner, Bramsen, Wengel and Quay described RNAi-active molecules having discontinued guide (or antisense) strands. In fact, Bramsen and Wengel indicated that duplexes designed to contain discontinuities in the guide strands completely eliminated silencing of the target.
The mechanistic difference between miRNA-mediated RNAi and siRNA-mediated RNAi can make certain modifications and/or designs suitable for one but not the other. Thus, there remains a heightened interest in formulating new and advantageous design features suitable for miRNA mimetics.